1. Field of the Invention
The present invention relates to acoustic transport members used for transmitting sound waves utilized in an acoustic keyboard system to provide information representative of a key selected. More particularly, this invention relates to improvements in the acoustic transport member over the construction disclosed in U.S. applications identified by: Ser. No. 087,854 entitled "Acoustic Encoding Apparatus", filed Oct. 24, 1979 which is a continuation of application Ser. No. 853,778 filed Nov. 21, 1977 now abandoned; Ser. No. 892,814 entitled "Multi-Bar Encoding Apparatus Utilizing Acoustic Energy", filed Apr. 3, 1978 now U.S. Pat. No. 4,258,356, both invented by Vincent P. Jalbert, and particularly a copending application Ser. No. 246,820 invented by Raymond A. Pajer et al entitled "Encoding Apparatus Utilizing Acoustic Waves of Controlled Polarity", filed on even date herewith. The three above-mentioned applications have the same assignee as the present application. To the extent appropriate to the present invention, the disclosures of the above-identified U.S. applications are incorporated herein by reference.
2. Description of the Prior Art
Keyboards of the acoustic type have been demonstrated to be a successful advancement in the art, especially those keyboards used in conjunction with an encoding apparatus. Generally, acoustic keyboards employ sound inducing key means that operate to launch sound waves within an acoustic transport member assembled in the acoustic keyboard. These sound waves provide information e.g., elapsed time measured by circuitry and used to produce a discrete coded representation of the selected key. Examples of acoustic systems having keyboard input are fully outlined in the above-mentioned applications U.S. Pat. No. 4,258,356, and simultaneously filed copending application of Raymond A. Pajer et al, (hereinafter referred to as prior applications I, II and III, respectively). Another example of an acoustic system using a member for transporting sound waves is disclosed in United Kingdom Pat. No. 1,386,070, granted to Roger Bennison, published Mar. 5, 1975 and entitled "Pressure Actuated Signalling Means". These acoustic systems all employ a form of an acoustic member capable of transporting sound waves. Yet, in the art there is a continued search to improve the reliability of these acoustic systems, particularly in the development of an acoustic member fabricated to sustain the intensity of the sound wave signal over the distance they travel within the acoustic member as pointed out below.
In prior copending application I and the British Patent of Roger Bennison, the acoustic transport member disclosed is an elongated continuous cylindrical rod. The disclosed straight rod successfully transports sound waves, however lacks structure defining discrete impact points from which sound waves are emitted in response to key actuation. A well-defined impact point is necessary for ensuing encoding circuitry to accurately determine the key position selected along the rod. Accordingly, these two acoustic systems are sensitive to the lateral positioning of the sound inducing keys along the member. It has been found that sideways displacement of the sound inducing device with respect to the rod changes the intended impact location along the member and thereby introduces an acoustical variable in the system.
In prior application II, there is disclosed a different acoustic system based on sensing sound waves transmitted through a plurality of acoustic transport members. The acoustic principle disclosed in this system improves on the accuracy and reliability of known acoustic systems, however it is more complex and costly to implement. The acoustic members in prior application II are structured to include distinct impact points in the form of tabs pre-positioned along the member. Each acoustic member is generally a bar supporting the tabs in a longitudinal relationship according to the spacing of the sound-inducing strikers. These tabs provide the necessary structure on the member to afford lateral stability with respect to the strikers contacting the bar at precisely the same location along the bar with each actuation.
While the acoustic member with tabs (prior application II) is a considerable improvement over the previously straight rod members, in terms of laterally fixing the impact points in relationship with one another along the member, the multiple tabbed bars have been found to produce sound wave signals lacking in intensity compared to those generated within the straight rod over the same distance.
Copending application III discloses an acoustic transport member fabricated with specially-shaped teeth or dissimilar tabs that generate sound waves having a particular polarity combination different among adjacent impact points (tabs). As a result, this acoustic system produces a set of signals within a single acoustic member that are readily and accurately distinguishable for proper functioning by encoding devices even in the presence of acoustic variables effecting the intensity of the sound waves when received by sound wave sensing and converting transducers coupled on the member.
In using the toothed member of copending application III, it was discovered that sound waves originating from near one end of the member produced a set of sound waves that when received by their respective transducer were significantly different in intensity levels based on the distance each is required to travel. In other words, the wave traveling the shorter distance is much higher in intensity than the wave forced to travel to the far end of the member. The reason for dissimilar intensity levels is attributed to dispersion or a scattering of the wave form in passage (lengthwise) through the member. Dispersion is believed to be primarily caused by the propagating waves entering enlarged areas represented by the tabs and being reflected off discontinuously orientated surfaces presented by the tab ends with respect to the intended direction of wave movement towards the transducers. Though the acoustic system repeatedly functioned properly with dissimilar wave intensities when tested in a laboratory environment, it is felt that this condition could cause marginal operation of the encoding device over a period of time and in consideration of high volume production. Accordingly, there is a need for improving the toothed acoustic transport member in an effort to equalize sound wave intensity sensed at each end of the member for safety sake.